Spatial Modeling of Maximum Capacity Values of Irrecoverable Rainfall Retention by Forests in a Small Watershed

With hydrologic calculations being performed, the most important factor in forming and estimating rainfall runoff is the actual amount of rain precipitations flowing under the tree canopies of the taiga zone. This is due to the fact that only a portion of rainfall reaching the soil through the forest canopy takes part in river runoff formation. At present, in the understanding of hydrological processes there is no unanimity on methods of estimating rainfall retention by the canopies of different tree species in various natural geographical zones. The existing estimation methods rely on empirical observations of net and gross rainfall rather than on the results of physical modeling of moisture on leaf surfaces in droplet form. The disadvantage of the methods existing in the world is that it is not possible to make a spatial estimation of rainfall captured by canopies. The purpose of this study is mapping of maximum rainfall interception capacity for a small forest watershed. Rainfall is retained on a canopy in droplet form (droplet size varies from 10.6 to 18.6 mg). Specific water retention (mass per unit leaf surface area) is determined by the leaf (needle) roughness. The overall droplet retention on canopies is determined by leaf surface area and precipitation intensity. The maximum mass of rainfall retention on the canopies of individual deciduous trees reaches 77 kg, (3.0-4.0 mm per canopy projection area) and that of coniferous trees is from 24.8 to 58.0 kg (1.9 to 5.9 mm). Taking into account rainfall losses for canopy interception makes it possible to reduce the margin of error in calculations of maximum rainfall flood loss from 126 to 25%.